Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude 17.0 x 10^–22C/m². What is E: (a) in the outer region of the first plate, (b) in the outer region of second plate, and (c) between the plates?

(a) To the left of the plates, electric fields are equal and opposite as plates are close to each other electric field is zero as surface charge density in outer side is zero. 

(b) To the right of the plates, electric fields are equal and opposite as plates are close to each other electric field is zero. 

(c) Electric fields between the plates are in same direction as total E.F. on both sides of plate due to $\mathrm{\sigma }$ surface charge density = $\frac{\mathrm{\sigma }}{{\mathrm{\epsilon }}_0}$
So, electric field of inner side of plate  = $\frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0}$
and for both plate   $\mathrm{E} = \frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0}+\frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0}$
                              $\mathrm{E} = \frac{\mathrm{\sigma }}{{\mathrm{\epsilon }}_0} = \mathrm{\sigma } \times 4\mathrm{\pi } \times 9 \times {10}^9$              $\mathrm{E} = 17.0 \times {10}^{-22}\times 4 \times 3.14 \times 9 \times {10}^9$ 

$$\begin{gathered} \mathrm{E} = 1921.7 \times {10}^{-13} \\ = 1.92 \times {10}^{-10}\mathrm{N}/\mathrm{C}. \end{gathered}$$